Switch point phenotypes and recruitment across complex life cycles: Role of size- and density-dependent processes

Background/Question/Methods

For organisms with complex life histories, environments encountered early in ontogeny may substantially alter densities or phenotypes transitioning into subsequent habitats. These differences in initial conditions could arise via a number of processes, including differences in maternal investment or habitat selection, abiotic factors, or the lethal and phenotypic effects of predators earlier in ontogeny. In this study we employ a simulation based approach to extend the ‘minimize mortality (μ)/growth (g)’ framework of Werner and Gilliam (1984) to understand how effects early in ontogeny shape survival and subsequent switch point phenotypes.  While previous models predict optimal switch points as a function of size-specific growth and mortality in each stage or habitat, for many taxa, these vital rates depend upon density, as well as size.  
Results/Conclusions

Here, we incorporate both density-dependent processes and variation in initial phenotypic and density conditions to elucidate the relative importance of density- and size dependence in vital rates on survival and size and timing of subsequent life history switch points.  We show that initial cohort density and phenotype can affect how size- and density-specific processes in later stages magnify or reduce variation earlier in ontogeny.  Our results highlight the importance of density dependence for determining both survival and the timing of life history switch points.